1. Field of the Invention
The present invention relates to an image forming apparatus having a colorimetric function and a colorimetric apparatus.
2. Description of the Related Art
Multi-color image forming apparatuses for forming multi-color images are required to form images with stable tints on recording materials for a long period of time. In order to satisfy this request, it is conceivable to form a plurality of patterns having different colors on a recording material, measure the colors using a colorimeter, and provide feedback to image forming conditions (Japanese Patent Laid-Open Nos. 2005-292431 and 2006-11205).
Japanese Patent Laid-Open No. 2005-292431 proposes an apparatus in which two conveyance guides sandwich a recording material therebetween in order to stabilize the attitude of the recording material during colorimetric measurement. Accordingly, a driving source for driving the conveyance guides becomes necessary. Furthermore, Japanese Patent Laid-Open No. 2006-11205 describes an apparatus in which a color sensor is projected into a conveyance path and is brought into contact with a recording material when detecting a test pattern, and the color sensor is withdrawn from the conveyance path when not detecting a test pattern. That is to say, the color sensor and a recording material are usually separated from each other, and are closer to each other only during colorimetric measurement. Compared with Japanese Patent Laid-Open No. 2005-292431, Japanese Patent Laid-Open No. 2006-11205 is advantageous in that one of the conveyance guides can be omitted because the function thereof is performed by the color sensor.
However, according to the invention of Japanese Patent Laid-Open No. 2006-11205, the color sensor and a biasing plate facing the color sensor are separated from each other when not detecting a test pattern, and, thus, the color sensor may be contaminated with floating residual paper dust, dust from the outside, and the like. Contamination of the color sensor lowers the precision of the colorimetric measurement (reduces the light amount and increases the stray light amount), thereby making it difficult to suppress a change in the tint. Note that, during colorimetric measurement, a recording material passes through a point between the color sensor and the biasing plate while keeping contact therewith, and, thus, a colorimetric window part of the color sensor can be cleaned. However, if cleaning intervals are prolonged, the contamination level progresses, and passing of only one sheet of recording material on which a test pattern has been formed may not be sufficient to clean the measurement window.